Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

879
FXUS63 KLOT 271722
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1122 AM CST Fri Feb 27 2026

.KEY MESSAGES...

- Dense freezing fog this morning will affect the commute in the
  Chicago metro area.

- Today will be unseasonably warm and breezy with a threat for
  rapid brush fire spread.

- A pair of storm systems may bring accumulating snow to parts
  of the area this weekend, favoring areas near and north of the
  Wisconsin state line Saturday afternoon, and areas south of
  Interstate 80 Sunday night.

- There is a growing signal for an active stretch featuring
  periods of showers and possibly thunderstorms mid to late next
  week and beyond, likely accompanied by much above average
  temperatures at times.

&&

.UPDATE...
Issued at 619 AM CST Fri Feb 27 2026

Opted for a short fused Dense Fog Advisory in the Chicago metro.
Strengthening southwest flow aloft has advected the overnight
fog bank northeastward and it`s gotten noticeably thicker on
webcams (and here outside the NWS office in Romeoville).
Considering that a moving shallow dense fog bank can be quite
hazardous for drivers, with the Friday morning rush upon us,
decided on the advisory (vs. continued special weather statement
issuance). The advisory is in effect until 9 AM, though it`s
possible the worst conditions improve earlier in the 8 AM hour.
Within the city of Chicago, warming conditions downtown may help
keep the lowest visibility a few miles inland of the lakeshore.

Castro/Petr

RC

&&

.DISCUSSION...
Issued at 350 AM CST Fri Feb 27 2026

Through Sunday Night:

Light winds and clear skies have allowed shallow fog to develop
mainly southwest of the Chicago metro in Illinois early this
morning. Below freezing temperatures temperatures could also
lead to patchy slide spots developing where fog has become
locally dense. Given the shallow and patchy nature of the fog,
have opted to handle this with an SPS through 7 AM CST but a
consideration for a Dense Fog Advisory may become warranted if
the dense areal coverage increases toward daybreak. Expect any
lingering fog to erode within an hour or two of sunrise.

We are headed for an unseasonably warm day today with strong
southwest winds developing in response to a sub-1000 mb low
moving across Ontario. Strong warm advection paired with deep
mixing will allow temperatures to warm into the 60s across the
area. In fact, some areas southwest of the Chicago metro could
potentially approach or even reach 70F if the most deeply mixed
guidance (HRRR/RAP) verifies. The depth of mixing will also play
a crucial role in the upper bounds of wind gusts and lower
bounds for the dewpoint/relative humidity, all important factors
when assessing the potential for rapid spread of brush fires
(more details on this can be found in the Fire Weather section
below). HRRR and RAP remain fairly consistent in a brief window
when winds could gust to 35-40+ mph for a few hours late in the
afternoon before easing around sunset as winds turn west to
northwest behind a cold front.

Attention then turns to a low amplitude shortwave expected to
dive out of Canada toward the Upper Midwest on Saturday. This
clipper-system may bring a period of f-gen driven accumulating
snow somewhere in the region Saturday afternoon into the early
evening; however, big question marks remain as to where this
band ends up tracking. The latest forecast leans toward the
more northerly guidance which keeps the center of the snow band
north of the WI-IL stateline. There remain a few solutions with
a farther south track which would take this band across
northern Illinois. Forecast vertical profiles also suggest that
there could be convective snow shower elements south of the main
band of snow, which would include northern Illinois into
northwest Indiana even with a more northerly track provided
that there is sufficient saturation. Thus, opted to maintain
snow chances across the area (20-50%), highest near the WI-IL
state line. The temperature forecast on Saturday will also
largely driven by the position of this band of snow which could
result in a sharp gradient in temperatures across the local
area, from as low as 30s north to 50s to around 60 well south of
I-80.

Yet another system will follow on the heels of the first
bringing the potential for accumulating snow to the region
Sunday night. Similar to the first system there remains a lot
of uncertainty in the system track. The latest blended guidance
continues to have highest snow chances for areas south of I-80
toward central IL/IN. An expansive surface high that sets up
across the Upper Midwest and broader Great Lakes region could
help shift the northern periphery of the snow farther south,
which some of the global guidance has been starting to catch
onto, though the ECMWF remains the farthest north. With
temperatures in the 20s any snow that does fall would readily
accumulate on untreated surfaces. Will continue to monitor
trends over the coming days. Stay tuned!

Petr


Monday through Thursday (and beyond):

While the month of February will finish up solidly above normal
temperature wise, it still featured predominantly northwest flow
aloft, resulting in well below average precipitation (and
snowfall). This will change in a big way during the upcoming
first week of March following a seasonably chilly first couple
days of the month (possibly accompanied by some snow in spots).
The pattern will transition to the negative phase of the Pacific
North American (PNA) teleconnection pattern, characterized by
western CONUS troughing and eastern CONUS ridging at the mid and
upper levels. Such a pattern is commonly active locally, which
should entail periods of beneficial precipitation as we head into
the growing season.

Also notable in the upcoming pattern is the lack of any
corresponding high latitude blocking in the Arctic and North
Atlantic (positive Arctic Oscillation/AO and North Atlantic
Oscillation/NAO). This will allow for the eastern ridging to
become particularly pronounced, suggesting a generally above to
well above average temperature regime possibly persisting all the
way through mid March. However, in the early spring, even in a
mild pattern, individual storm tracks play a large role in
temperature distributions, as the chilly waters of Lake Michigan
result in notably cooler temps in onshore flow north of storm
tracks and/or reinforced warm fronts.

Turning from the big picture teleconnection pattern to the day to
day, specific details are rather murky given a large range of
solutions offered by the various ensemble solutions. The northward
extent of an active baroclinic zone will be modulated by the
proximity of surface high pressure to the region, which is quite
variable between the ensemble systems and across ensemble members.
An initial round of precipitation could reach into at least
portions of the area in the Monday night-Tuesday timeframe, with
the overall highest PoPs south of I-80. This could feature some
threat for wintry precip as surface wetbulb temps may still be
flirting with freezing.

Variance only increases into the mid to late workweek timeframe,
lowering confidence in most of the specific details. The main
exception to this is for rain being the predominant ptype with
high confidence in the Wednesday-Friday period next week. In
general, the GEFS is faster in bringing rain back to the area
during the day on Wednesday and into Wednesday night, while the
the foreign produced ensemble systems are more focused on the
Wednesday night and Thursday timeframe. Regardless of exactly how
the mid to late week period evolves, precipitable water of
250-300% of average/normal for early March could certainly spell
corridors of heavy rainfall and an associated flooding threat.
The extent (or lack thereof) of embedded thunderstorms will likely
play a role as well, though for now, the forecast does not yet
feature any explicit mention for thunderstorm chances. Finally,
the exceptionally mild and moist cyclone warm sectors in the
upcoming pattern may also feature a threat for organized strong to
severe convection within in the general region.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1122 AM CST Fri Feb 27 2026

Forecast concerns for the terminals...

- Gusty southwest winds this afternoon with gusts around 25-35
  kts expected.

- Period of flurries and light snow showers Saturday afternoon,
  mainly near the IL-WI line.


The earlier fog has burned off with mostly sunny skies expected
for the rest of the afternoon. Winds have also been steadily
increasing as mixing has commenced which will allow
southwesterly gusts to peak around 25-35 kts this afternoon.
While gusts will begin to subside after sunset, a cold front
will move through the area tonight which may allow a few lower
20 kt gusts to persist through midnight. Thereafter, winds will
turn northerly through the night with speeds around 8-10 kts
expect.

Heading into Saturday, a shortwave disturbance will pivot across
the upper Midwest and northern Great Lakes which will lead to
the development of a band of snow. Latest forecast trends are
for this band of snow to stay in southern WI but forecast
soundings do show some decent mid-level saturation which could
result in a couple of flurries/light snow showers at the
terminals towards midday and through Saturday afternoon.
However, due to the dry low-levels confidence on snow shower
coverage is low. So for now have opted to introduce PROB30s for
flurries at RFD, ORD, and MDW (DPA and GYY omitted due to snow
arriving after their TAF periods). If snow does occur the modest
temperatures (around 33-35F) should limit any accumulations to
maybe a dusting on grassy surfaces.

Regardless, ceilings should lower into the 4000-5000 ft range
Saturday afternoon with some MVFR clouds possible especially if
snow occurs. Otherwise, expect winds to become easterly Saturday
morning with speeds around 10-12 kts through the rest of the
TAF period.

Yack

&&

.FIRE WEATHER...
Issued at 350 AM CST Fri Feb 27 2026

Threat for brush fire spread this afternoon...

Strong southwesterly winds are expected to develop across the
region this afternoon. At this point, our forecast favors
sustained winds increasing toward 15 mph and gusts ranging from
30 to 35 mph late morning through early afternoon. If more
aggressive mixing scenarios pan out, sustained winds could
exceed 20 mph and gusts could exceed 40 mph for a brief 2 to 3
hour window late in the afternoon. When paired with
unseasonably warm temperatures in the low to mid 60s and
afternoon minimum relative humidity values of 25 to 30 percent,
conditions may approach Red Flag Warning criteria on a localized
basis, particularly southwest of the Chicago metro area.

Borchardt/Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 9 PM CST this evening for Winthrop
     Harbor IL to Gary IN.

     Small Craft Advisory until 9 PM CST this evening for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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